Ultrathin low-frequency sound absorbing panels based on coplanar spiral tubes or coplanar Helmholtz resonators

TLDR

Classic sound absorbers require a thickness of at least one‑quarter wavelength to achieve full absorption. The study presents ultrathin panels that absorb sound energy with a thickness about one percent of wavelength. The panels are fabricated by bending and coiling quarter‑wavelength tubes into 2D coplanar structures embedded in a matrix, using 3D printing. The panels’ sound‑absorption efficacy was confirmed by close agreement between theoretical predictions and experimental measurements.

Abstract

Performance of classic sound absorbing materials strictly depends on their thickness, with a minimum of one-quarter wavelength to reach full sound absorption. In this paper, we report ultrathin sound absorbing panels that completely absorb sound energy with a thickness around one percent of wavelength. The strategy is to bend and coil up quarter-wavelength sound damping tubes into 2D coplanar ones, and embed them into a matrix to form sound absorbing panel. Samples have been designed and fabricated by 3D printing. Efficacies of sound absorption by these panels were validated through good agreement between theoretical analysis and experimental measurements.